I. Field of the Invention
The present invention relates to Code Division Multiple Access (CDMA) systems. More particularly, the present invention includes, but is not limited to, a novel and improved CDMA base station that controls transmit power based on quadrature signal calculations.
II. Description of the Related Art
Code Division Multiple Access (CDMA) technology is commonly used in communications systems. In a typical CDMA system, a CDMA base station transmits a CDMA signal to numerous CDMA communications devices, such as wireless telephones. The CDMA signal is comprised of numerous individual user signals. The CDMA base station generates the CDMA signal by encoding each individual user signal with a unique spreading sequence, such as a pseudo random sequence. The CDMA base station then adds the encoded user signals together to form the CDMA signal.
In a CDMA system, individual user signals are not separated based on frequency or time, but are spread across the entire frequency band. Each CDMA communications device derives its particular user signal based on the unique spreading sequence. Due to this combination of multiple signals encoded with random sequences, the CDMA signal has special power concerns because each signal represents noise to the other signals that share the frequency band. Thus, CDMA transmission systems must carefully track the power of each signal.
Baseband CDMA signals are typically generated in a well-known quadrature format comprised of quadrature CDMA signals I and Q. Quadrature CDMA signals I and Q are transmitted using carriers of the same frequency, but in phase quadrature. In other words, an RF CDMA signal can be constructed by modulating I by cosine (2xc3x97pixc3x97frequencyxc3x97time) and by modulating Q by sine (2xc3x97pixc3x97frequencyxc3x97time). In IS-95A, quadrature signals carry the same data with different pseudo-random sequence codes.
FIG. 1 depicts a multi-sector base station 100 that is currently known in the art. The base station 100 is divided into geographic sectors with callers A-F in sector 1 and callers G-L in sector 2. For the sake of illustration, caller F will move from sector 1 to sector 2 as indicated by the dashed lines, but the operation of the base station 100 is first discussed prior to the caller F move from sector 1 to sector 2. Those skilled in the art will appreciate that the diagram of the base station 100 has been simplified for clarity.
The sector 1 portion of the base station 100 includes cell site modems 102 and 104, gain control 106, summing circuit 108, CDMA signal processor 110 including gain 112, and antenna 114. The sector 2 portion of the base station 100 includes cell site modems 122 and 124, gain control 126, summing circuit 128, CDMA signal processor 130 including gain 132, and antenna 134.
In operation, the cell site modem 102 receives signals for callers A, B, C and applies conventional CDMA processing to generate CDMA quadrature signals I and Q. The cell site modem 102 provides the CDMA quadrature signals I and Q to the summing circuit 108. The cell site modem 104 receives signals for callers D, E, F and applies conventional CDMA processing to generate CDMA quadrature signals I and Q. The cell site modem 104 provides the CDMA quadrature signals I and Q to the summing circuit 108. The summing circuit separately combines the I signals and the Q signals and transfers them to the CDMA signal processor 110. The CDMA signal processor 110 performs analog conversion, filtering, up-conversion, and amplification to provide a Radio Frequency (RF) CDMA signal to the antenna 114. The antenna 114 transmits the RF CDMA signal 116 over the air to the callers A-F in sector 1.
The cell site modem 122 receives signals for callers G, H, I and applies conventional CDMA processing to generate CDMA quadrature signals I and Q. The cell site modem 122 provides the CDMA quadrature signals I and Q to the summing circuit 128. The cell site modem 124 receives signals for callers J, K, L and applies conventional CDMA processing to generate CDMA quadrature signals I and Q. The cell site modem 124 provides the CDMA quadrature signals I and Q to the summing circuit 128. The summing circuit separately combines the I signals and the Q signals and transfers them to the CDMA signal processor 130. The CDMA signal processor 130 performs analog conversion, filtering, up-conversion, and amplification to provide an RF CDMA signal to the antenna 134. The antenna 134 transmits the RF CDMA signal 136 over the air to the callers G-L in sector 2.
Each cell cite modem 102, 104, 122, and 124 provides gain information 118 to both the gain control 106 and the gain control 126. The gain information 118 includes the squared gain for each call, pilot signal, and overhead. Gain control 106 and gain control 126 each maintain a database that incorporates the gain information 118.
The CDMA signal processor 110 monitors the transmit power (Pout) of the CDMA signal 116 for sector 1 and provides a Pout value 119 for sector 1 to the gain control 106. The gain control 106 compares the Pout value 119 for the CDMA signal 116 to a Gain Value (GV) equal to the sum of the squared gains for the CDMA signal 116. The squared gains for the CDMA signal 116 are obtained from the gain information 118. The gain control 106 transfers a control signal 117 to the gain 112 to adjust the Pout to maintain a ratio of GV to Pout at a pre-determined value. FIG. 2 shows the desired relationship between Pout and the GV. The points X and Y represent operational measurements, and the arrows represent the control applied through the control signal 117 to the gain 112 to maintain the pre-determined value. Those skilled in the art are aware that the slope of the pre-determined value blossoms during start-up and wilts during shut-down.
The CDMA signal processor 130 monitors the Pout for sector 2 and provides the Pout value 139 for sector 2 to the gain control 126. The gain control 126 compares the Pout value 139 for the CDMA signal 136 to a GV equal to the sum of the squared gains for the CDMA signal 136. The squared gains for the CDMA signal 136 are obtained from the gain information 118. The gain control 126 transfers a control signal 137 to the gain 132 to adjust Pout to maintain a ratio of GV to Pout at a predetermined value.
When caller F moves from sector 1 to sector 2, the cell site modem 104 for sector 1 transfers the caller F quadrature signals 141 and 142 to the summing circuit 128 for sector 2. Thus, the CDMA signal 136 now includes the caller F signal. As a result, the gain control 126 must now add the square of the caller F gain to its GV.
It should be appreciated that each cell site modem must transfer all gain information 118 to the gain control in each sector. This requires a data transfer arrangement across all sectors, and much of the transferred data is unnecessary. For example, gain control 126 does not need the gain for caller A unless caller A moves into sector 2. The gain control for each sector must also track the calls in its sector and perform repeated calculations based on a changing database. The current power calculation technique for CDMA base stations should be improved to reduce data transfer and storage.
The above-described problem is solved with CDMA quadrature signal technology that controls the transmit power of a CDMA signal. The CDMA quadrature signal technology eliminates unnecessary data transfer and storage because gain control is accomplished without transferring or using per call gain information. The CDMA quadrature signal technology receives a CDMA signal, and in response, processes quadrature components of the CDMA signal to generate a power control signal. The CDMA quadrature signal technology adjusts the gain of the CDMA signal in response to the power control signal. A CDMA transmitter transmits the CDMA signal after the gain is adjusted. One example of the CDMA transmitter is a CDMA base station. Using the invention, a multi-sector CDMA base station can control power without transferring gain information to base station components for all sectors.
In some examples of the invention, a multi-sector base station squares and sums the quadrature I and Q signals in a CDMA signal for a given sector. A ratio is then formed by comparing the sum to the transmit power of the CDMA signal. The transmit power of the CDMA signal is controlled to move the ratio closer to a pre-determined value that optimizes base station performance.